Pumps and the like must be coupled to a driver component, usually an electric motor, in order to drive or turn the pump shaft. To do this, a coupling is connected between the pump and driver which transmits torque from the driver to the pump. It is important that the centerline of the pump is perfectly aligned with the centerline of the driver, otherwise problems can arise including, for example, extreme heat and gear wear in the coupling, cracked or failed shafts from the constant flexing of the rotating shaft, overheating and fatigue problems, uneven face loading with stationary design mechanical seals and excessive axial movement of rotating design seals. Although a coupling can compensate for axial growth of the shaft due to thrusting or thermal growth, its cannot compensate for radial misalignment between the pump and driver. Thus, radial misalignment must be corrected by other means.
Two popular alignment methods being used in industry include the reverse indicator method and laser aligning. With the reverse indicator method, alignment is done in three stages: determining where the components are located in relationship to each other; calculating what has to be moved and how far to make the centerline of the pump line up with the centerline of the driver; and moving the hardware, usually the driver. Laser aligning utilizes laser equipment which does an excellent job of making the measurements and calculating the amount of movement necessary, but one still has to move the hardware which is usually the most difficult part of alignment, in part, because of the lack of jack bolts on smaller pumps.
The task of aligning the centerlines of coupled hardware becomes more difficult when the surface on which hardware is to be mounted uneven. Typically, an appropriate combination of metal shims have to be placed between the mounting feet of a piece of equipment and the surface on which the equipment is mounted. This way, the piece of equipment can be raised and lowered as required to match the centerline of the equipment with the centerline of a motor or driver to which the equipment is coupled. For example, if a motor is coupled to a pump and the motor is too high or too low, thin metal shims are installed or removed to place the motor's centerline in alignment with the centerline of the pump.
Once a piece of equipment is mounted and aligned, over time the feet of the equipment can rust, leaving pits and irregularities in the feet. Further, it is not uncommon for the feet to settle into a warped state. Pitting and warping of the feet can lead to an unsatisfactory condition where the equipment becomes misaligned with a motor to which it is coupled. Since it is typically too expensive or impractical to replace or resurface such feet, additional shims are usually installed to restore alignment of the equipment and motor. As a result, the shim thickness between the various feet of the equipment can begin to vary greatly creating the potential for another misalignment situation called angular soft/foot. Angular soft/foot affects the thickness of a shim causing a shim having a constant thickness to deform into a shim of irregular thickness. This is a difficult problem to overcome since shims are designed only to take up space between two parallel surfaces. There is a procedure used occasionally for resolving angular soft/foot known as step shimming. Step shimming involves staggering shims underneath a foot and maneuvering a wedge between the foot and shim. However, this often results in an arrangement where very little surface contact exists between the foot and its mounting surface.